1. Field of the Invention
This invention relates in general to devices for ultrasonically testing structures for flaws, and in particular to a nozzle assembly for discharging a stream of water onto the structure, the nozzle assembly holding a transducer for emitting and receiving ultrasonic waves.
2. Description of the Prior Art
Inspection of advanced composite structures often requires the use of ultrasonic water squirter systems. These systems usually utilize through-transmission techniques to detect delamination and other internal flaws. In a through-transmission water squirter system, a nozzle discharges a stream of water against the structure. The nozzle contains a transducer which transmits ultrasonic sound waves. A receiver will be placed on the other side of the structure to receive the sound waves. The through-transmission techniques are useful in detecting the presence of internal flaws and delaminations, but cannot provide information as to the through-wall thickness location of the flaw.
In another technique, a pulse-echo squirter system is used. In this technique, the transducer both transmits and receives the sound pulse. A pulse-echo squirter system has the capability to both detect and locate in the through-wall dimension the presence of delaminations. However, in the past, the turbulence usually generated in water squirter systems has made it difficult to conduct pulse-echo inspections. This is especially true for finding near surface defects.
Many efforts have been undertaken to develop an ultrasonic squirter system which would provide a signal-to-noise level sufficient to allow the use of pulse-echo techniques and provide an acceptable near surface resolution capability. The prior art efforts have been primarily focused upon the reduction of turbulence in the water stream. Several designs have taken the approach of using baffle plates in the water stream which are drilled with numerous small holes. The intent of this approach is to reduce the Reynolds number and thereby produce a laminar flow. Others have used devices resembling electrical heat sinks which are inserted downstream of the transducer with the intention of reducing the turbulence of the flow.